Coronary angioplasty is a medical procedure used to treat blocked coronary arteries as an alternative to a coronary bypass operation. It involves the insertion of a balloon catheter into the blocked artery and the inflation of the balloon to expand the size of the artery and relieve the blockage. While the procedure is often effective in opening the artery, one problem is the tendency of the artery to reclose. This requires that the angioplasty procedure be repeated which is obviously expensive and may be risky for the patient.
In recent years, small cylindrical tubes called stents have been inserted into the artery after a coronary angioplasty procedure. The stents are made of a thin-walled metallic material and have a pattern of apertures or holes cut around the circumference of the stent along most of its length. The purpose of the stent is to reinforce the walls of the artery after an angioplasty to prevent reclosing of the artery or to at least prolong the time the artery takes to reclose. The pattern in a stent is typically cut by a laser cutting tool.
In manufacturing stents, basic lathe techniques have been adapted to support the tubing used to form the stent during the hole cutting process. Typically, a piece of tubing is supported between a drive mechanism and a tail stock support in the manner of a lathe. A laser cutting tool positioned above the tubing will cut the pattern by moving relative to the tubing along the length of the finished stent, the tubing being rotated as necessary to present different parts of the circumference to the laser cutting tool. After the pattern is completely cut in the stent, the tubing is cut first at the tail stock end and then at the drive end of the stent to allow a finished stent to be completed.
This manufacturing method has various limitations which results in a fairly high scrap rate. For example, because the pattern typically occupies a large percentage of the surface area of the stent, the stent may sag or bow downwardly during the cutting process as the pattern is cut and the cut area becomes larger. This is particularly true for thin walled material of the type most desirably used to form stents. In addition, friction from the tail stock mechanism often cause manufacturing errors throughout the part. Accordingly, many stents are rejected as failing to meet the necessary cut accuracy when manufactured by the methods used prior to this invention.
Another difficulty is alignment of the drive mechanism and tail stock support with the laser cutting tool. These items are not directly coupled to one another. Accordingly, if any of the drive mechanism, tail stock support, or laser cutting tool are bumped or jarred during the manufacturing operation, further errors will occur. This is a further contributing factor to the relatively high scrap rate of these devices.